The invention relates to a method of controlling a motor vehicle that is equipped with an automated clutch device, with an engine that is actuated by an engine control device, preferably with an actuator-controlled automated transmission, and with at least one electronic control device that controls the actuation of the transmission and the clutch device. The method includes detecting a quantity that is at least representative of a traveling speed of the vehicle, detecting an actuation of a brake and/or of an energy- or fuel-metering element, and detecting a condition of the engine. In a case where neither the brake pedal nor the fuel-metering element is found to be actuated while the engine is running and the vehicle speed exceeds a given limit value, the clutch is taken out of engagement.
A transmission or a transmission device, as the term is used herein, is a mechanism that can be shifted or set to different shift positions or ratio positions, either in steps or in a stepless range, where the transmission produces different transmission ratios between two rotary shafts. The transmission device can be configured as a stepwise shifting transmission or as a steplessly settable transmission, such as for example a cone-pulley transmission or the like. Shift processes of the transmission device between different ratio steps can be performed automatically or manually or in a partially automated way, or automated with the added optional possibility for manual intervention. In the shift from one shift position to another shift position, there can be an interruption in vehicle traction, or the transmission may also be of a kind that works with no interruption in vehicle traction.
The term “automated shift transmission” as used in the context of the present invention means in particular a transmission device in which the shift processes can be actuated in an automated manner where there is an interruption in vehicle traction. The automated shift transmission has for example at least one controllable electric motor or a hydraulic device for the actuation of shift processes.
A gear level or shift level in the sense of the present invention means a shift position in which a given transmission ratio is set. Furthermore, the term transmission ratio may be used synonymously with gear level in the sense that a steplessly settable transmission may be used instead of a transmission with discrete ratio steps.
Methods and devices of the kinds that have just been referred to belong to the known state of the art and are used in motor vehicles with automated shift transmissions that can be equipped with a so-called free-running function. The term free-running refers to a condition where the clutch is disengaged while the vehicle is coasting, where neither the gas pedal as fuel metering element nor the brake pedal is used. Essentially, the purpose of the free-running function is to save fuel. In this operating state, the vehicle is traveling or rolling, i.e., the vehicle speed is greater than zero, while the engine rpm-rate is about equal or exactly equal to the idling rpm-rate, or the engine may even be switched off. To enter the free-running mode (also referred to herein as free-running function), the clutch is moved out of engagement under the control of the electronic control unit while the transmission remains in gear, so that the vehicle does not lose kinetic energy as a result of the braking effect of the engine. The free-running mode is usually terminated by applying a brake and/or the gas pedal.
In the context of electronic control and regulating. devices with associated sensors and actuating means as well as methods for the control and regulation of motor vehicles with automated shift transmissions, reference is made to DE 40 11 850 A1, DE 44 26 260 A1, and DE 195 07 622 A1.
The free-running function of the foregoing description has the drawback that when the free-running mode is ended, the re-engagement of the clutch cannot always be performed in a jolt-free, quick and comfortable manner.
Automated clutch systems with a hydraulic actuating means for the clutch, as well as control methods relating to such systems, are disclosed in particular in DE 44 26 260 A1. Furthermore, a hydraulically operated automated transmission with an automated clutch is disclosed in WO 97/10456. In DE 44 26 260, an actuating means is disclosed with a piston that is movable in a cylinder by hydraulic action. The cylinder has an opening, the so-called snifting bore that serves to equalize the pressure and volume of the hydraulic fluid when the piston is in a position where the snifting bore is open. In this position of the piston, the fluid volume in the cylinder communicates through a hydraulic conduit with a fluid volume in a reservoir container so that a volume adjustment can take place. However, the piston can take this position only when the clutch is engaged, i.e., in the non-actuated position. The invention is further related to DE 44 26 260, whose content is hereby expressly incorporated herein by reference.
It is a further disadvantage that the pressure- and volume adjustment—since it requires the clutch to be in the engaged condition—cannot be performed during the free-running mode, because the control unit takes the clutch out of engagement during the free-running mode.